I imagine that the writers of Cowboys and Aliens had a grand old time inserting into their screenplay as many as possible of both Westerns and sci-fi/horror cliches. They did very well: there's a loner cowboy with cigarillo and fists of steel, a domineering cattleman and his feckless son, a timid barkeep, a posse on horseback tracking abducted relatives a la The Searchers, a band of Chiricuara Apaches fighting for their own survival, innocent distressed maidens, etc., etc., and at the end, a hero riding off into the sunset. On the other side of the ledger, computer graphic aliens resembling the velociraptors in Jurassic Park (except for the slimy green blood) attacking us poor mortals, multiple abductions, and o my gosh even a little boy hiding from a creepy creature in a crevice in the rock, and then our intrepid James Bond-y macho hero sneaking into the spaceship to free the captives and dynamite the mother ship, my o my what a bounty.
And to these cliches, the unsatisfied writers added a bonus -- a dollop of movie amnesia. Why not? Jake Lonergan awakes in the desert not knowing who he is, why he is wounded, and without a clue as to why he has a futuristic bracelet soldered to his wrist. Like most movie amnesiacs, he remains fully functional and unimpaired. He's not the least bit agitated by his loss of memory. But then comes a truly embarrassing, semi-racist moment. The Indians, who as everyone knows are noble and in touch with the human soul in a way that we products of western civilization can never be, treat his amnesia with a frothy brew (perhaps mescaline, but who can tell?). Memory spontaneously returns; Jake remembers that he escaped from the mother ship, knows where it has been parked, and also knows about the secret entrance. And so to work.
Later on, the released abductees are all amnesiac, but they're cured instantly (the movie is long enough) without Apache influence.
So now we can add alien abduction to the long list of precipitants of movie amnesia.
This film could have been a gas except that its makers forgot about the comedy that's inherent in the title and in the conception. Too bad. As it stands, it's a solemn, noisy, elaborate, expensive, flimsy chimera.
At one point in the quest, the posse comes across an enormous structure that looks like a paddle-wheeler right there in the middle of the desert. "There's no river within five hundred miles that can handle that thing." But they continue along, the boat is never mentioned again and plays no part in the story -- thereby proving that even screenwriters can suffer disabling bouts of amnesia.